Technical Field
The present invention relates to a device, a method, and a program for generating a virtual endoscopic image that shows the interior of a body cavity of a subject for assisting endoscopic observation during surgery, examination etc., using an endoscope inserted into the body cavity of the subject.
Background Art
Endoscopic surgeries, such as laparoscopic surgery and thoracoscopic surgery, are drawing attention in recent years. The endoscopic surgery has an advantage in that the burden imposed on the patient is quite small since it can be conducted by forming only a few incisions of several centimeters for inserting an endoscope and a surgical tool, without requiring laparotomy or thoracotomy. On the other hand, conducting a surgery under a limited field of view of the endoscope is highly difficult in view of skill and requires a highly-skilled operating surgeon. If a blood vessel or an organ of the patient is erroneously damaged and bleeds during an endoscopic surgery, the manner of surgery has to be changed to one using a conventional technique involving laparotomy or thoracotomy.
On the other hand, a virtual endoscope technique for generating an image that is similar to an endoscopic image from a three-dimensional volume image obtained by imaging with a CT apparatus, or the like, is known. This technique is popular in North America as a method for finding a tumor, in particular, a tumor in the large intestine by CT imaging without performing an endoscopic examination. Further, a technique for safely and quickly performing an endoscopic surgery, examination, or the like, using a virtual endoscopic image is proposed.
For example, Japanese Unexamined Patent Publication No. 2002-263053 (hereinafter, Patent Document 1) teaches a device that detects the position of the endoscope with a sensor to determine the detected position as a view point, generates a virtual endoscopic image having a wider angle of view than that of the endoscope, and displays a real endoscopic image obtained by endoscopic imaging and the virtual endoscopic image superimposed one on the other.
However, although the technique taught in Patent Document 1 allows compensating for the narrow field of view of the endoscope with a virtual endoscopic image, the virtual endoscopic image has the same view point and the same observation direction as those of the real endoscopic image, and a part of interest, such as a target of surgery, may not be shown in the virtual endoscopic image or the real endoscopic image depending on the positional relationship between the part of interest and the endoscope, making it difficult to understand the positional relationship between the endoscope and the part of interest.
In order to address this problem, Japanese Unexamined Patent Publication No. 2011-212245 (hereinafter, Patent Document 2), for example, proposes a technique where a color template for changing the color of a virtual endoscopic image depending on the distance from the view point position of a virtual endoscope is defined for each structure, and the color of each structure is changed depending on the distance from the view point. Further, Japanese Unexamined Patent Publication No. 2011-212244 (hereinafter, Patent Document 3) proposes a technique where a color template defining an opacity for each structure to display a semi-transparent image of each part, in order to prevent such a situation that a structure of interest is not shown when another structure is present between the view point position of a virtual endoscope and the structure of interest.